The ability to move our arms and legs depends on the integrity of our upper and lower motor neurons, which relay electrical signals from our brain to our muscles. When motor neurons die, as occurs after injury or in a variety of degenerative diseases that affect primarily infants and children (spinal muscular atrophies) or adults (amyotrophic lateral sclerosis (ALS)), irreversible paralysis ensues. In order to develop better ways to treat these clinical conditions, I propose to investigate the signaling mechanisms that normally promote motor neuron survival and how these pathways may go awry in disease. The Barres lab has developed methods to purify and culture defined types of CNS neurons including spinal motor neurons (SMNs). Using these methods, they recently discovered that elevation of cAMP alone is sufficient to strongly promote the survival of SMNs, even in the absence of peptide trophic factors. I will investigate the signaling pathways that enable cAMP to promote survival, specifically focusing on the hypothesis that the newly described B-raf signaling pathway is involved. Second, I will test the hypothesis that spinal motor neurons survive after axotomy because their cAMP levels become elevated, allowing them to survive in the absence of their usual peptide trophic inputs from muscle and Schwann cells. I will also study whether elevation of cAMP levels will prevent SMNs from dying in a transgenic mouse model of ALS. Lastly, I will devise a novel technique utilizing adenoviral vectors and immunopanning to purify and culture upper motor neurons in order to investigate the signals that promote their survival in vitro. By defining the signaling mechanisms involved in upper and lower motor neuron survival in culture and in animal models my goal is to develop new strategies to treat patients with spinal cord injuries and motor neuron diseases.